Physics Formula Sheet: What to Memorise vs What to Derive for Classes 11-12

Physics in Classes 11 and 12 often feels like an endless memory test. Faced with hundreds of equations across mechanics, electromagnetism, and modern physics, students make one of two critical mistakes: they try to rote-learn every single expression, or they attempt to derive everything in the exam hall and run out of time.

Success in CBSE, ICSE, state boards, JEE, and NEET depends on a systematic split: core results must be hardwired into your memory, while intermediate steps and conditional relations must be derived quickly.

The Golden Rule for Indian Competitive and Board Exams

Time is your scarcest resource. In a JEE Main or NEET paper, you have less than two minutes per question. In a CBSE or ICSE board exam, lengthy derivations eat into your writing and revision time if you do not know standard shortcuts.

The strategy is simple:

• Memorise: Fundamental definitions, universal constants, end-result formulas that cannot be derived within 15 seconds, and standard approximation forms.
• Derive: Intermediary expressions, sign-convention variations, and geometry-dependent formulas that stem directly from core laws.

What You Must Memorise (The Core Arsenal)

Certain formulas appear so frequently that hesitation will cost you marks. These must be on the tip of your tongue before you walk into any exam hall.

Mechanics (Class 11)

• Equations of motion under uniform acceleration: $v = u + at, \quad s = ut + \frac{1}{2}at^2, \quad v^2 = u^2 + 2as$
• Centripetal acceleration: $a_c = \frac{v^2}{r} = \omega^2 r$
• Work-energy theorem and potential energy functions (gravitational and spring).
• Moment of inertia for standard symmetric bodies (ring, disc, solid sphere, hollow sphere, rod).

Electrodynamics and Magnetism (Class 12)

• Coulomb's Law and Electric Field due to a point charge: $\vec{E} = \frac{1}{4\pi\varepsilon_0}\frac{q}{r^2}\hat{r}$
• Ohm’s Law micro-form and macroscopic resistance definition: $R = \rho \frac{l}{A}$
• Magnetic force on a moving charge and a current-carrying wire: $\vec{F} = q(\vec{v} \times \vec{B}), \quad \vec{F} = I(\vec{l} \times \vec{B})$
• Inductance and Reactance formulas for AC circuits: $X_L = \omega L, \quad X_C = \frac{1}{\omega C}, \quad Z = \sqrt{R^2 + (X_L - X_C)^2}$

Optics and Modern Physics

• Lens Maker's Formula and Thin Lens formula: $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$
• De Broglie wavelength: $\lambda = \frac{h}{p} = \frac{h}{\sqrt{2mE}}$
• Radioactive decay law: $N(t) = N_0 e^{-\lambda t}, \quad T_{1/2} = \frac{\ln 2}{\lambda}$

What You Must Derive (On the Spot or in Rough Work)

If you waste space in your memory bank on these, you risk displacing vital core formulas. Practice deriving them until you can recreate them in under 30 seconds.

| Topic | Formula to Derive | Base Principle to Remember | | :--- | :--- | :--- | | Electrostatics | Electric field due to an infinite line charge or sheet | Gauss’s Law ($\oint \vec{E} \cdot d\vec{A} = \frac{q_{\text{enclosed}}}{\varepsilon_0}$) | | Current Electricity | Equivalent resistance of complex infinite ladders | Symmetry and recursive node substitution | | Magnetism | Magnetic field at the center of a circular arc or axis of a coil | Biot-Savart Law ($d\vec{B} = \frac{\mu_0 I}{4\pi}\frac{dl \sin\theta}{r^2}$) | | Ray Optics | Mirror formula for concave/convex mirrors | Similar triangles and Snell's Law geometry | | SHM | Time period of a physical pendulum or U-tube liquid column | Restoring torque/force equation ($\tau = -I\alpha$ or $F = -kx$) |

Exam-Specific Applications: Boards vs. Entrance Tests

Your approach to formula sheets must adapt to the exam pattern you are targeting under the 2026-27 syllabus guidelines:

• For CBSE and ICSE Board Exams: Examiners award step marks. Memorising final shortcuts will get you the right answer in Section A (MCQs), but long-answer sections require you to show the complete derivation from fundamental laws (like Gauss's law or Ampere's circuital law). Do not skip practicing derivations in writing.
• For JEE Main and Advanced: Derivations are rarely asked directly. Here, understanding boundary conditions matters more. Memorise how formulas change when mediums change (e.g., how capacitance changes when a dielectric slab of thickness $t$ is introduced).
• For NEET: Speed is everything. Create a formula sheet that includes standard shortcut ratios (e.g., how time period changes when a spring is cut into $n$ parts). Never waste time deriving standard results during a NEET physics section.

Quick Checklist

Before you finalise your personal formula notebook for Classes 11 and 12, run through this quick checklist:

• [ ] Have I listed all universal constants (Planck’s constant, permittivity of free space, gravitational constant) with their standard units?
• [ ] Are vector forms clearly separated from scalar magnitude formulas?
• [ ] Have I explicitly written out the sign conventions for optics and thermodynamics?
• [ ] Can I derive Gauss’s law applications and Biot-Savart applications without looking at a textbook?
• [ ] Are dimensional formulas for derived quantities (like torque, permittivity, magnetic flux) verified?

Build your formula sheet actively as you finish each chapter rather than downloading a generic printout. What you write with your own hand stays in your head when the exam timer starts.